Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$79.81	3.738%	$82.7933	$82.79	$82.80	$82.80
Purchase #2	$90.33	8.744%	$98.2285	$98.23	$98.25	$98.20
Purchase #3	$118.58	11.688%	$132.4396	$132.44	$132.45	$132.40
Purchase #4	$225.27	12.778%	$254.055	$254.06	$254.05	$254.10
Purchase #5	$42.64	9.839%	$46.8353	$46.84	$46.85	$46.80
Purchase #6	$144.31	10.107%	$158.8954	$158.90	$158.90	$158.90
Purchase #7	$131.28	8.398%	$142.3049	$142.30	$142.30	$142.30
7 purchase totals =	$832.22		$915.5520	$915.56	$915.60	$915.50